\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{circuitikz}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\ctikzset{bipoles/length=1cm}
\begin{document}
\small
\begin{circuitikz}[>=latex, scale=1.2,european]
  % \useasboundingbox(0.9,0)rectangle(5.1,5);
  \draw (-3,0)node[left]{$A$}--(3,0)node[right]{$C$} to [R=$R_x$,*-*] (0,1.1)node[above]{$B$} to [R=$R$,*-*] (-3,0);
  \draw (-3,0)--(-3,-0.7) to [cute open switch] (-1,-0.7) to [battery] (1,-0.7)	to [pR,name=hb] (3,-0.7)--(3,0)	;
  \draw(1,-0.7)--(1,-0.7|-hb.wiper)--(hb.wiper);
  \draw (1,-0.7) [fill=black] circle (1.2pt);
  \draw (0,1.1) to [rmeter, t=G] (0,0.25);
  \draw [->](0,0.25)--(-.5,.25)--(-.5,0)node[below]{$D$};
  \node at (-1.75,0) [below]{$\ell_1$};
  \node at (1.25,0) [below]{$\ell_2$};
\end{circuitikz}
\end{document}